The ongoing development of communication (e.g. telephone) systems and associated components has resulted in the integration of high speed digital processing devices with conventional analog components and systems. Because the electrical and electronic signal levels of analog and digital devices differ significantly from each other (e.g. +/-48 VDC for analog telephone equipment and +5 VDC for digital signal processing/control devices), integrated systems are often fitted with separate power supplies, each dedicated to a respective application.
Proposals to limit the hardware intensity associated with the use of separate power supplies have included multi-capability power supply units, that may be selectively configurable by the user, as by means of jumper cables or switches, to accommodate operating the power supply from either an (117V) AC source, or a DC source. Because such power supply units require intervention by either the user or a craftsperson, their installation and use is labor intensive. Moreover, the range of input sources from which such units may be powered is ordinarily limited to a relatively small ratio (e.g. on the order of 2:1), so that the complexity (and therefore cost) of the hardware is not insubstantial.